The invention relates to a water activatable layer on a substrate, to methods for producing a substrate containing a water activatable layer and to laminates made using a material containing a water activatable layer.
Relatively inexpensive novelty items containing hidden images are produced in large quantities and are used in a variety of applications including game pieces, food packaging prizes, educational children""s books and the like. Many of these items contain full color hidden images. The images may be developed or revealed by applying a developer or solvent to the hidden image area of the object. The disadvantage of many of these items is that the object can only be used once, and once the image is revealed, the object no longer has significant appeal. Another disadvantage of such objects is that the developer or solvent is often toxic or hazardous and thus could be dangerous when used by unsupervised children or infants.
In order to overcome the problems associated with the use of toxic developers or solvents, objects containing water activatable coatings were developed. When dry, the coatings are substantially opaque and thus effectively hide an underlying image from view. However, upon wetting the coating with water, the underlying image is revealed or is provided with full vibrant color. Once the object again dries, the coating becomes opaque and thus again hides the image from view. While such objects and image developers are less toxic than the solvents and developers used for other latent image objects, it is difficult to produce such objects in a cost effective manner in quantities which enable reasonable profits to the manufacturers and distributors thereof.
Despite the advances in the art of printing hidden or latent images, there remains a need for a cost effect material and method for applying the material to a substance to produce vibrant full color images upon activation.
Considering the foregoing, the present invention provides an in-line method for making a water-activatable laminate. According to the method, a polymeric film having a first surface and a second surface is provided. An opaque water activatable material containing from about 5 to about 40 wt. % pigment and from about 60 to about 95 wt. % binder is applied to the first surface of the film using an in-line coating technique selected from a flexographic coater, a rotary screen press, and a rotogravure coating technique. The coating is then dried to provide a single water activatable opaque layer having a thickness ranging from about 0.60 mil to about 2.0 mil. The binder for the opaque coating layer includes a mixture of solvent, butyl acetate, ethylene glycol monobutyl ether and propylene glycol.
An important advantage of the invention is that only a single opaque layer is required for hiding the underlying image. Unlike prior art techniques which require the use of a black or dark pigment, the opaque layer of the invention is devoid of such black or dark pigments. Also, the opaque coating may be produced in high volume using the techniques described herein. Another advantage of the invention is that the opaque coated film may be applied to a variety of substrates containing images which may be black and white or full color images. Still another advantage of the invention is that the image containing substrate and film containing an opaque layer may be produced separately in the same or remote locations and combined later into a single composite material, and the opaque coating may be produced in high volume using the techniques described herein.